Optical nano-antennas are antennas with dimensions of less than the optical wavelength of the received light and operate to respond to the received light based on surface plasmon polaritons (SPP) to produce highly localized and enhanced electric fields at nanoscale, i.e., subwavelength “hotspots” around or at such optical nano-antennas. Optical nano-antennas can be used for converting EM radiation into confined/enhanced fields at or in a nanoscale structure for various applications for sensing, imaging, energy conversion and others.